Activated carbon is useful for the purification of drinking water by the removal by adsorption and absorption of undesired substances from the drinking water. However, activated carbon particles have a rough, porous texture which is capable of providing a favorable and protected environmental surface for bacterial growth (note "Pilot Plant Testing of Activated Carbon and Adsorption Systems" by Patrick R. Cairo, et al., Journal of American Water Works Association, November, 1979, Part 1, pages 660-673.) As a result, algae or bacteria colonize the carbon surface, thus diminishing the surface available to contact the water.
Even if the water to be filtered is chlorinated, some bacteria are chlorine resistant and furthermore, when using activated carbon for the treatment of the water, it is found that the top layer of the activated carbon can actually remove the chlorine so effectively that bacteria grow in the lower layers thereof. Thus, the activated carbon actually can promote the growth of bacteria that would not grow in the chlorinated water per se. The most predominate bacteria that were isolated belonged to the genus Pseudomonas. In addition, bacteria of the genus Baccilus were also found in large quantity.
U.S. Pat. No. 3,325,402 of Erskine teaches the purification of water or other fluids by passing the same through a filter mass of granular activated carbon which has adsorbed thereon a water soluble antimicrobial quaternary ammonium salt. These salts are only physically contained within the pores of the activated carbon and quickly become leached out so that the antimicrobial effectiveness disappears after a short time. The leaching process itself results in elevated germicide levels of the effluent rendering it impure, and in fact often in violation of the Safe Drinking Water Act standards by virtue of the presence of the leached germicide.
The need therefore exists for a suitable means of purifying water and other liquids using an antimicrobial agent which remains effective over prolonged periods of time and long usage.